I have a removable Hard DRIVE that was set up on my old computer, A COMPACTS Presario (OS/XP). I'm now tyring to use it in a HD Pavilion (Also XP). I 'm using it for music recording. It's in a Lian Li R10f Mobile Rack pull out rack. It worked fine in the Presario. But, I pull the whole thing out to install it. But, now it says unallocated when I try to install it in EITHER computer. You could try doing a repair while its connected, not too sure why this is happing.  It may or may not work but something too try if nothing else.Right click My Computer and select Manage...then Disk Management.
Right click the drive in question and select Properties...
Report back with your findings.Well, properties says "This divice is working properly". But, disk manager says "Not Initialized / Unallocated". But, If I initialize it will it erase the disk?Yes.
It was probably disconnected prematurely and i'm afraid the data would be gone in this case anyways...
You could try some data recovery apps on it.
Best of Luck.or currpted an may not be able to recover it.  You could try doubt it would work.I afraid your probably right. THANK you both.